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United States Patent |
5,283,946
|
Simmons
,   et al.
|
February 8, 1994
|
Method and apparatus for forming metal leads
Abstract
The excise and lead form of TAB leads bonded to an integrated circuit chip.
Leads extending beyond a sidewall are clamped between a first clamp and a
form anvil at a first portion spaced from the chip. The leads are also
clamped between an excise/form tool and a second clamp at a second portion
spaced further from the chip than the first portion. An excise blade cuts
the leads outside the second portion. Then the excise/form tool, second
clamp and excise blade move downwards in a curved path toward the chip to
form a first lead corner against the form anvil and a second lead corner
against the excise/form tool without splaying or galling the leads.
Inventors:
|
Simmons; Richard L. (Jonestown, TX);
Wehrly, Jr.; James D. (Austin, TX);
Bertram; Michael J. (Austin, TX)
|
Assignee:
|
Microelectronics And Computer Technology Corporation (Austin, TX)
|
Appl. No.:
|
062876 |
Filed:
|
May 17, 1993 |
Current U.S. Class: |
29/827; 29/566.2; 29/566.3; 72/427; 72/428; 140/105; 140/147; 257/E23.049 |
Intern'l Class: |
H01R 043/00 |
Field of Search: |
29/827,566.1,566.2,566.3
140/105,147
72/427,428
174/52.4
83/146,635
|
References Cited
U.S. Patent Documents
Re28582 | Oct., 1975 | Dammar.
| |
2997907 | Aug., 1961 | Constantino | 83/635.
|
3417643 | Dec., 1968 | Bennett | 83/146.
|
4064917 | Dec., 1977 | Diaz | 140/105.
|
4103718 | Aug., 1978 | Steigerwald | 140/105.
|
4361173 | Nov., 1982 | Storimans | 140/1.
|
4371012 | Feb., 1983 | Weresch | 140/105.
|
4390598 | Jun., 1983 | Phy | 428/577.
|
4399610 | Aug., 1983 | Moyer | 29/827.
|
4488581 | Dec., 1984 | Stumpf et al. | 140/147.
|
4553420 | Nov., 1985 | Fierkens et al. | 72/380.
|
4559978 | Dec., 1985 | Glatzel | 140/147.
|
4602661 | Dec., 1986 | Heller et al. | 140/105.
|
4625772 | Dec., 1986 | Maskens | 140/105.
|
4627159 | Dec., 1986 | Waldner | 29/827.
|
4633920 | Jan., 1987 | Donovan et al. | 140/105.
|
4691747 | Sep., 1987 | Sokolovsky | 140/147.
|
4763401 | Aug., 1988 | Marinoni et al. | 29/868.
|
4787426 | Dec., 1988 | Linker et al. | 140/147.
|
4816427 | Mar., 1989 | Dennis | 29/827.
|
4829669 | May., 1989 | Nakajima | 29/874.
|
4945954 | Aug., 1990 | Wehrly, Jr. et al. | 140/105.
|
5065504 | Nov., 1991 | Olla | 29/827.
|
Foreign Patent Documents |
61-69158 | Apr., 1986 | JP | 29/827.
|
3-22467 | Jan., 1991 | JP | 29/827.
|
3-129863 | Jun., 1991 | JP | 29/827.
|
Other References
U.S. Patent Re-issue 28,582 filed Oct. 28, 1975 by Dammar
"Comparative Compliance of Generic Lead Designs for Surface Mounted
Components" by Robert T. Kotlowitz, AT&T Bell Laboratories, Whippany, New
Jersey 07981, pp. 7-19.
|
Primary Examiner: Arbes; Carl J.
Attorney, Agent or Firm: Sigmond; David M.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation of co-pending U.S. application Ser. No. 07/817,214
filed Jan. 6, 1992, now U.S. Pat. No. 5,210,936.
Claims
What is claimed is:
1. A method of excising and forming a plurality of metal leads connected to
a device, comprising the steps of:
clamping a first portion of the leads spaced from the device by contacting
the top of the first portion with the bottom surface of a first lead clamp
and the bottom of the first portion with the top surface of a form anvil,
said form anvil further comprising a forming edge between the top surface
and a forming surface on the side opposite the device;
clamping a second portion of the leads further from the device than the
first portion and spaced from the first portion by contacting the top of
the second portion with the bottom surface of an excise/form tool and
contacting the bottom of the second portion with the top surface of a
second lead clamp, said excise/form tool further comprising a forming
surface on the side facing the device, an outer surface on the side
opposite the device and a forming edge between the bottom surface and the
forming surface, and said second lead clamp further comprising an outer
surface on the side opposite the device, wherein the outer surfaces of the
excise/form tool and second lead clamp are aligned;
excising a third portion of the leads further from the device than the
second portion which extends beyond the outer surfaces of the excise/form
tool and second lead clamp, thereby forming outer lead ends;
moving the excise/form tool and second lead clamp downwards and toward the
device until a fourth portion of the leads between the first and second
portions is moved through an arc between the forming surfaces of the form
anvil and the excise/form tool, thereby bending the leads at the forming
edge of the form anvil to form a first corner in the leads and at the
forming edge of the excise/form tool to form a second corner in the leads;
and
releasing the leads from the first lead clamp, form anvil, form/excise
tool, and second lead clamp.
2. A method of forming metal leads, comprising the steps of:
providing a plurality of metal leads terminating at inner and outer ends,
the inner ends connected to a base, the leads comprising a first portion
spaced from the base, a second portion spaced further from the base than
the first portion, and a third portion between the first and second
portions;
removably securing the first portion of the leads against a first form
anvil therebelow, the first form anvil comprising (i) a first forming
surface facing the outer ends of the leads, and (ii) a first forming edge
between the first forming surface and the first portion of the leads;
removably securing the second portion of the leads against a second form
anvil thereabove, the second forming anvil comprising (i) a second forming
surface facing the inner ends of the leads, and (ii) a second forming edge
between the second forming surface and the second portion of the leads;
then
moving the form anvils toward each other such that the third portion of the
leads moves through an arc between the forming surfaces so as to bend the
leads at the first forming edge and at the second forming edge thereby
forming respective first and second corners in the leads; and then
releasing the leads from the form anvils.
3. The method as recited in claim 2 wherein the form anvils are moved
toward each other by holding the first form anvil stationary while moving
the second form anvil downwards and toward the first form anvil.
4. The method as recited in claim 2 wherein the arc is a curved path with
continually decreasing radius.
5. The method of claim 2 wherein the form anvils are moved toward each
other until the third portion of the leads is clamped between the forming
surfaces.
6. The method of claim 2 wherein the outer ends of the leads are formed by
excising the leads after the leads are removably secured against the
second form anvil.
7. The method of claim 2 wherein the surfaces of the anvils in contact with
the leads are flat and horizontally disposed, the forming surfaces are
flat and vertically disposed, and before bending the leads the leads are
flat and horizontally disposed.
8. The method of claim 7 wherein the leads are bent simultaneously, the
leads are released simultaneously, and after the leads are released the
first portion of the leads is substantially horizontal, the second portion
of the leads is substantially horizontal, and the third portion of the
leads is substantially vertical.
9. The method of claim 8 wherein the base is a releasably secured
electronic device and the leads extend beyond a sidewall of the device.
10. The method as recited in claim 9 wherein the electronic device is an
integrated circuit chip with a rectangular top surface and four peripheral
sidewalls, the leads are flexible elongated tape-automated-bonding leads
with flat upper and lower surfaces extending beyond one of the sidewalls,
the inner ends of the leads are bonded to pads on the top surface of the
chip, and prior to bending the leads the leads are coplanar with the top
surface of the chip.
11. The method of claim 10 wherein the outer ends of the leads are formed
by excising the leads after the leads are removably secured against the
form anvils but before the leads are bent.
12. The method of claim 2, including
releasably securing the first portion of the leads by contacting the top of
the first portion of the leads with the bottom surface of a first lead
clamp and contacting the bottom of the first portion of the leads with the
top surface of the first form anvil thereby clamping the first portion of
the leads between the first lead clamp and the first form anvil;
releasably securing the second portion of the leads by contacting the
bottom of the second portion of the leads with the top surface of a second
lead clamp and contacting the top of the second portion of the leads with
the bottom surface of the second form anvil thereby clamping the second
portion of the leads between the second lead clamp and the second form
anvil; and
releasably the leads from the clamps and anvils after bending the leads.
13. The method of claim 12 wherein
the second form anvil and second lead clamp contain outer surfaces that are
aligned with each another, are adjacent to the leads at a portion further
from the base than the second portion of the leads, and are facing away
from the inner ends of the leads; and
the outer ends are excised by a blade which slidingly engages at least one
of the outer surfaces before cutting the leads adjacent to the outer
surfaces and then slidingly engages at least one of the outer surfaces
after cutting the leads.
14. A method of forming metal leads, comprising the steps of:
providing a plurality of metal leads comprising inner leads connected to a
base, unconnected outer ends, a first portion spaced from the base, a
second portion spaced further from the base than the first portion, and a
third portion between the first and second portions;
providing a first form anvil having a horizontal top surface, a first
vertical forming surface, and a first forming edge therebetween;
providing a second form anvil having a horizontal top surface, a second
vertical forming surface, and a second forming edge therebetween;
removably securing the bottom surface of the first portion of the leads
against the top surface of the first form anvil such that the first
forming edge is adjacent to the first portion of the leads and the first
forming surface faces the outer ends of the leads;
removably securing the top surface of the second portion of the leads
against the bottom surface of the second form anvil such that the second
forming edge is adjacent to the second portion of the leads and the second
forming surface faces the inner ends of the leads;
moving the form anvils toward each other such that the third portion of the
leads moves through an arc between the forming surfaces so as to bend the
leads at the first forming edge and at the second forming edge thereby
forming first and second corners, respectively, in the leads; and then
releasing the leads from the form anvils.
15. An apparatus for excising and forming a plurality of metal leads
connected to a device, comprising the steps of:
means for clamping a first portion of the leads spaced from the device by
contacting the top of the first portion with the bottom surface of a first
lead clamp and the bottom of the first portion with the top surface of a
form anvil, said form anvil further comprising a forming edge between the
top surface and a forming surface of the side opposite the device;
means for clamping a second portion of the leads further from the device
than the first portion and spaced from the first portion by contacting the
top of the second portion with the bottom surface of an excise/form tool
and contacting the bottom of the second portion with the top surface of a
second lead clamp, said excise/form tool further comprising a forming
surface on the side facing the device and an outer surface on the side
opposite the device and a forming edge between the bottom surface and the
forming surface, and said second lead clamp further comprising an outer
surface on the side opposite the device, wherein the outer surfaces of the
excise/form tool and second lead clamp are aligned;
means for excising a third portion of the leads further from the device
than the second portion which extends beyond the outer surfaces of the
excise/form tool and second lead clamp for forming outer lead ends;
means for moving the excise/form tool, second lead clamp and excise blade
downwards and toward the device in a curved path until a fourth portion of
the leads between the first and second lead corners is moved through an
arc between the forming surfaces of the form anvil and the excise/form
tool in order to bend a first corner in the leads at the forming edge of
the form anvil and a second corner of the leads at the forming edge of the
excise/form tool; and
means for releasing the leads from the first lead clamp, form anvil,
form/excise tool, and second lead clamp.
16. An apparatus for forming metal leads terminating at inner and outer
ends, the leads comprising inner ends connected to a base, a first portion
spaced from the base, a second portion spaced further from the base than
the first portion, and a third portion between the first and second
portions, wherein the apparatus comprises:
a first form anvil comprising a first forming surface facing the outer ends
of the leads, and a first forming edge between the first forming surface
and the first portion of the leads;
a second form anvil comprising a second forming surface facing the inner
ends of the leads, and a second forming edge between the second forming
surface and the second portion of the leads;
means for removably securing the bottom surface of the first portion of the
leads against the first form anvil;
means for removably securing the top surface of the second portion of the
leads against the second form anvil;
means for moving the form anvils toward each other such that the third
portion of the leads moves through an arc between the forming surfaces so
as to bend the leads at the first forming edge and at the second forming
edge thereby forming respective first and second corners in the leads; and
means for releasing the leads from the form anvils after the leads are
bent.
17. An apparatus for forming metal leads, the leads comprising inner ends
connected to a base, unconnected outer ends, a first portion spaced from
the base, a second portion spaced further from the base than the first
portion, and a third portion between the first and second portions;
a first form anvil having a horizontal top surface, a first vertical
forming surface, and a first forming edge therebetween;
a second form anvil having a horizontal top surface, a second vertical
forming surface, and a second forming edge therebetween;
means for removably securing the bottom surface of the first portion of the
leads against the top surface of the first form anvil such that the first
forming edge is adjacent to the first portion of the leads and the first
forming surface faces the outer ends of the leads;
means for removably securing the top surface of the second portion of the
leads against the bottom surface of the second form anvil such that the
second forming edge is adjacent to the second portion of the leads and the
second forming surface faces the inner ends of the leads;
means for moving the form anvils toward each other such that the third
portion of the leads moves through an arc between the forming surfaces so
as to bend the leads at the first forming edge and at the second forming
edge thereby forming first and second corners, respectively, in the leads;
and
means for releasing the leads from the form anvils.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to forming metal leads, and more particularly to
flexible techniques for excising and forming metal leads bonded to an
electronic device which extend over a sidewall of the device.
2. Description of Related Art
In the manufacture of integrated circuits, silicon wafers containing many
individual integrated circuits are fabricated and then the wafers are cut
into individual integrated circuit chips or die. The chips are
subsequently packaged and interconnected to other electrical components.
During packaging, electrically conductive metal leads can be bonded
between a chip and an interconnect substrate to provide proper electrical
interconnection between different chips.
One technique for providing conductive interconnecting metal leads is
tape-automated-bonding (TAB). The leads can be fabricated on a continuous
carrier film in which the tape is a laminate of copper and a plastic
insulator and the leads are etched in the copper while on the plastic
carrier using well known etching processes. Or an additive metal
fabrication can be used. The film is normally perforated along the edges
with sprocket holes for use in advancement and alignment of the carrier
film. Individual chips can be electrically bonded to individual lead
frames in the tape, for instance by laser bonding as described in U.S.
Pat. No. 4,845,335, and the lead frames can be removed or excised from the
carrier film. Usually it is necessary to bend or form the leads prior to
bonding the outer lead ends to an interconnect substrate.
Conventional excise and lead form of TAB devices requires the design and
fabrication of custom tooling for each device size and/or lead form
geometry. These tools basically conform to punch and die technology where
the device is forced through a cutting die to excise it from a TAB film
strip, and then forced around a forming die to produce the lead form. See,
for instance, U.S. Pat. Nos. 2,997,907; 3,417,643; 4,064,917; 4,361,173;
4,371,012; 4,488,581: 4,559,978: 4,625,772; 4,633,920: 4,691,747;
4,787,426; 4,945,954 and 5,065,504.
As the pitch for TAB devices decreases (8 mils or less) it becomes more
difficult to maintain the outer lead pitch during the excise and lead form
operation. During excise sequence the device is literally punched through
a cutting die. The cutting allowance is either designed in with a
one-piece cutting die or adjustable with a four-piece cutting blade
matrix. If this cutting allowance is incorrect, burrs will form and often
cause lead splay.
Once excised from the TAB film strip, the leads become cantilevered beams
supported by the inner lead bond and often a dielectric support ring.
These lead beams have a very small cross-sectional area as compared to
their length, making them susceptible to bending. As these beams are
forced around a forming die, they are bent closest to the supported end
first and continually abraded down their length until the second or lower
bend is formed, making it difficult to control the pitch at the other end.
Keeper bars (strips of dielectric on the lead tips) are often used to
prevent splay on fine pitch devices; however, they may require more
complex form tooling and present other problems during outer lead bonding.
In addition, due to the tight tolerances required on fine pitch devices,
the punches and dies must be customized for the exacting specifications of
each TAB design. As a result, the tools are expensive, require long lead
times to procure, are labor intensive and are time consuming to install
and tune. Once on line, this is an effective and relatively fast (e.g., 6
to 8 seconds) method of excise and lead form. However, less static
activities such as the research and development of TAB multichip modules
may be hindered.
Needless to say, there is a need for an alternative approach to TAB excise
and lead form that allows an inexpensive set of hard tooling to be used
for a variety of chip sizes and beam tape geometries while minimizing
splaying and galling of the leads.
SUMMARY OF THE INVENTION
An object of the present invention is to provide excise and lead form of
TAB devices with varying sizes and lead geometries without the need to
change hand tooling. The present invention requires only a change in
programming to accommodate a wide variety of devices.
A feature of the present invention includes a method of excising and
forming a plurality of metal leads connected at inner ends to an
electronic device which extend beyond a sidewall of the device, comprising
the steps of clamping a first portion of the leads spaced from the device
by contacting the top of the first portion with the bottom surface of a
first lead clamp and the bottom of the first portion with the top surface
of a form anvil, said form anvil further comprising a forming edge between
the top surface and a forming surface on the side opposite the device,
clamping a second portion of the leads further from the device than the
first portion and spaced from the first portion by contacting the top of
the second portion with the bottom surface of an excise/form tool and
contacting the bottom of the second portion with the top surface of a
second lead clamp, said excise/form tool further comprising a forming
surface on the side facing the device and an outer surface on the side
opposite the device and a forming edge between the bottom surface and the
forming surface, and said second lead clamp further comprising an outer
surface on the side opposite the device, wherein the outer surfaces of the
excise/form tool and second lead clamp are aligned, excising a third
portion of the leads further from the device than the second portion which
extends beyond the outer surfaces of the excise/form tool and second lead
clamp, thereby forming outer lead ends, moving the excise/form tool and
second lead clamp downwards and toward the device until a fourth portion
of the leads between the first and second portions is moved through an arc
between the forming surfaces of the form anvil and the excise/form tool,
thereby bending the leads at the forming edge of the form anvil to form a
first corner in the leads and at the forming edge of the excise/form tool
to form a second corner in the leads, and releasing the leads from the
first lead clamp, form anvil, form/excise tool, and second lead clamp.
An advantage of the present invention is the use of one set of low cost
tooling which can rapidly adapt to a variety of device sizes and lead form
geometries.
Another advantage of the present invention is that the leads are not forced
around a forming die, but rather are clamped and bent at two programmable
points before excise and during lead form. This eliminates galling of the
vertical leg and minimizes splaying at the outer lead ends.
A still further advantage of the present invention is that the vertical leg
of the leads may contain a dielectric support bar, thereby decreasing the
footprint of the device and allowing closer chip-to-chip spacing.
Still another advantage of the present invention is the ability to perform
face-up and face-down lead forms with the same tooling.
These and other objects, features and advantages of the present invention
will be further described and more readily apparent from a review of the
detailed description and preferred embodiments which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description of the preferred embodiments can best be
understood when read in conjunction with the following drawings, wherein:
FIG. 1 shows a fragmentary enlarged elevational view of a prior art TAB
tape with an integrated circuit chip bonded to inner ends of metal TAB
leads,
FIGS. 2-11 show successive stages in cross-section of the excise and lead
form of TAB leads which extend beyond a sidewall of a chip in accordance
with the present invention,
FIG. 12 shows a perspective view of a chip after the TAB leads on all sides
have been excised and formed in accordance with the present invention,
FIG. 13 shows a cross-sectional view of the chip in FIG. 12 surface mounted
on a multi-chip module,
FIGS. 14-16 show side views of a prototype apparatus constructed in
accordance with the present invention,
FIG. 17 shows a top plan view of the apparatus in FIGS. 14-16, and
FIG. 18 shows an isometric view of the apparatus in FIGS. 14-16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the present invention will be described for purposes of illustration
only, by the excising and face-down forming of TAB leads bonded to an
integrated circuit chip, the present invention is applicable to excising
and forming other types of metal leads connected to electronic components.
Referring now to the drawings wherein depicted elements are not necessarily
shown to scale and wherein like or similar elements are designated by the
same reference numeral through the several views and, more particularly to
FIG. 1, the reference numeral 10 generally indicates a leadframe of a
tape-automated-bonding (TAB) tape having the usual sprocket holes 12 and a
plurality of metal leads 14 bonded at inner ends 16 to pads on top surface
18 of integrated circuit chip 20 having four peripheral sidewalls 22a,
22b, 22c and 22d. Polyimide support ring 24 in window 25 may be necessary
to keep leads 14 in place for assembly and test operations prior to
bonding the outer lead ends to a substrate.
With reference now to FIG. 2, there is seen a cross-sectional view of
system 26 for excising and forming TAB leads according to a particularly
preferred exemplification of the invention. Unless otherwise noted, all
surfaces are flat. Leadframe 10 can be fed into position using pins of a
pin plate (not shown) as alignment marks for sprocket holes 12. Though not
essential, a base may be positioned beneath chip 20. As may be seen,
preferably vacuum pipette 28 beneath chip 20 is raised vertically and
removably secures to the bottom 29 of chip 20 by applying a vacuum suction
pressure. Pipette 28 also assures that chip 20 is level and serves as a
reference point for other tooling. The leads 14 which extend beyond
sidewall 22a comprise first portions 30 spaced from chip 20 and second
portions 32 spaced further from chip 20 than first portions 30. The bottom
surface 34 of first lead clamp 36 is positioned above first lead portions
30, and the top surface 38 of form anvil 40 is positioned below first lead
portions 30. Form anvil 40 also includes forming surface 42 on the side
opposite chip 20, and curved forming edge 44 between surfaces 38 and 42.
Similarly, the bottom surface 46 of excise/form tool 48 is positioned
above second lead portions 32, and the top surface 50 of a spring loaded
second lead clamp 52 is positioned below second lead portions 32. Tool 48
also includes forming surface 54 on the side facing chip 20, outer surface
56 on the side opposite chip 20, curved forming edge 58 between surfaces
54 and 46, and cutting edge 60 between surfaces 46 and 56. Second lead
clamp 52 contains an outer surface 62 on the side opposite chip 20. Excise
blade 64 contains leading cutting edge 66 and sliding surface 68 adjacent
outer surface 62 of clamp 52. Sliding surface 68 and outer surface 62 are
aligned with outer surface 56, for example by a spring loaded nested cam
mechanism (one course, one fine) in excise/form tool 48 which can
precisely adjust the cutting allowance to provide near zero clearance
excising without burrs.
Referring now to FIGS. 3-4, the first lead portions 30 are clamped between
first lead clamp 36 and form anvil 40, and the second lead portions 32 are
clamped between excise/form tool 48 and second lead clamp 52. In FIG. 3,
first lead clamp 36 and excise/form tool 48 are lowered vertically until
their respective bottom surfaces 34 and 46 contact the tops of lead
portions 30 and 32, respectively. In FIG. 4, form anvil 40 and second lead
clamp 52 are raised vertically until their respective top surfaces 38 and
50 contact the bottoms of lead portions 30 and 32, respectively. Excise
blade 64 is also raised vertically with second lead clamp 52 but does not
yet slide or contact leads 14. Also, outer surfaces 56 and 62 are aligned
and form a smooth coplanar surface.
With reference now to FIG. 5, after the leads are clamped the excise
operation takes place. First lead clamp 36, form anvil 40, excise/form
tool 48 and second lead clamp 52 are held stationary while excise blade 64
moves upward in sliding contact with second lead clamp outer surface 62.
Excise blade 64 forces cutting edges 60 and 66 against third lead portions
70 further from chip 20 than portions 32. Third lead portions 70 reside on
the side of outer surfaces 56 and 62 opposite chip 20 and preferably
adjacent to outer surfaces 56 and 62. As excise blade 64 continues to move
upward and slidingly engages excise/form tool outer surface 56, cutting
edges 60 and 66 slice through leads 14 to form outer lead ends 72.
Referring now to FIGS. 6-8, the excised leads are bent into the specified
form. In FIG. 6, first lead clamp 36 and form anvil 40 remain stationary
while excise/form tool 48, second lead clamp 52 and excise blade 64 move
together downwards and toward chip 20 in a programmed path, as depicted by
arc 74. Leads 14 remain firmly clamped and are bent at first corners 76
and second corners 78. That is, first lead corners 76 are bent against
forming edge 44 of form anvil 40 whereas second lead corners 78 are bent
against forming edge 58 of excise/form tool 48. Since leads 14 are not
forced around a forming die the abrasive action common to conventional
forming is eliminated. Furthermore, the combination of lead clamping and
non-abrasive forming minimizes the chance of lead splay, thereby allowing
fine pitch devices to be lead formed without the use of a keeper bar. In
FIG. 7, excise/form tool 48 and second lead clamp 52 continue the
programmed motion in the direction of arc 74 to further bend corners 76
and 78. Arc 74 is preferably a curve with continually decreasing radius
from starting point 80 to finishing point 82 to avoid pulling or
stretching the leads as corners 76 and 78 are formed. A circularly curved
arc 74 is also generally suitable but a straight-line arc 74 is not. In
FIG. 8, fourth lead portions 84 between first and second lead portions 30
and 32, respectively, are moved through arc 74 and eventually sandwiched
between and pressed against forming surfaces 42 and 54. This temporarily
halts the motion of excise/form tool 48 and second lead clamp 52. For
illustration purposes, lead corners 76 and 78 are formed at substantially
90 degree angles, lead portions 84 are substantially vertical, lead
portions 86 between first corners 76 and inner lead ends 16 are
substantially horizontal, and lead portions 88 (which constitute the outer
lead bond foot) between second corners 78 and outer lead ends 72 are also
substantially horizontal. However, it is understood that lead corners 76
and 78 may be formed at any angle between 0 degrees and 90 degrees. For
instance, the motion of excise/form tool 48, second lead clamp 52 and
excise blade 64 could halt at the position shown in FIG. 7, resulting in a
greater leg angle and footprint. Furthermore, after the leads are released
from the tooling some "spring-back" shall occur. The amount the leads
spring-back depends on several factors such as the form radius and lead
metallurgy.
With reference now to FIGS. 9-11, the next step of the present invention is
to release leads 14 from the first lead clamp 36, form anvil 40,
excise/form tool 48, second lead clamp 52 and excise blade 64. In FIG. 9,
excise blade 64 is retracted to its initial position relative to second
lead clamp 52, and form anvil 40, second lead clamp 52 and excise blade 64
are lowered vertically while first lead clamp 36 and excise/form tool 48
remain stationary. In FIG. 10, excise/form tool 48, second lead clamp 52
and excise blade 64 are raised diagonally away from the leads while first
lead clamp 36 and form anvil 40 remain stationary until bottom surfaces 34
and 46 align. This precludes forming surface 54 on excise/form tool 48
from pulling-up on lead portions 84 and possibly deforming the leads. In
FIG. 11, first lead clamp 36 and excise/form tool 48 are raised vertically
while form anvil 40, second lead clamp 52 and excise blade 64 remain
stationary.
It is important to note that only the leads extending beyond sidewall 22a
of chip 20 have been excised and formed. Normally it will be necessary to
excise and form the leads on all sides of the device, as best seen in FIG.
12. This can be accomplished by next rotating any holding fixture or pin
plate (not shown) and vacuum pipette 28 by 90 degrees counterclockwise and
repeating the aforementioned steps to excise and form leads 14 extending
beyond sidewall 22b, and likewise for the leads 14 extending beyond
sidewalls 22c and 22d. With one side excised and formed at a time, the
total excise and form time for chip 20 is estimated on the order of 15-30
seconds. Alternatively, if desired, the leads 14 which extend beyond
opposite sidewalls 22a and 22c could be excised and formed simultaneously
using a separate first lead clamp 36, form anvil 40, excise/form tool 48,
second lead clamp 52 and excise blade 64 for each sidewall. Thereafter, a
pin plate and vacuum pipette 28 could be rotated 90 degrees, and the leads
14 extending beyond sidewalls 22b and 22d could also be excised and formed
in a similar manner. However, simultaneously forming leads 14 which extend
beyond adjacent sidewalls, e.g. sidewalls 22a and 22b, would not be
preferred since the reduced tool size would limit the tool's flexibility.
Referring now to FIG. 13, after each of leads 14 has been excised and
formed, chip 20 can be surface mounted on any interconnect media common to
TAB such as a multi-chip module copper/polyimide substrate 90 by bonding
outer lead ends 72 to bonding pads 92.
The positions and movements of vacuum pipette 28, clamp 36, form anvil 40,
excise/form tool 48, clamp 52 and blade 64 can all be controlled by a
programmable computer. This allows the TAB device to be excised at any
desired point along the length of the leads and consequently the lead form
may be placed at any desired distance from the edge of the chip.
Programmability also allows the geometry of the lead form to be changed by
simply changing the program without changing the hard tooling.
Because of this tooling flexibility, a variety of TAB devices can be
excised and lead formed without the down time of changing and setting up
new tooling. If a tooling change is needed, a new set of tooling with
smaller or larger blade width can be installed relatively quickly. This is
due to the simplicity of a one sided design in comparison to a four sided
punch and die set.
It should also be noted that the width of the cutting and forming blades
determines which devices can be excised and lead formed. These blades must
be able to span the width of the outer leads of the device, yet fit within
the dielectric window of the tape. For example, an excise blade width of
0.400 inches can be programmed to excise and lead form any TAB device with
an outer lead width (width of one side of the outer lead footprint) of
less than 0.400 inches and a dielectric window of greater than 0.400
inches.
PROTOTYPE APPARATUS
With reference now to FIGS. 14-18, a prototype apparatus generally
designated 100 was constructed by the Applicant to excise and lead form
TAB devices in accordance with the present invention. It is understood
that this example is meant to illustrate and not to limit the invention,
the scope of which is defined solely by the appended claims.
Referring now to FIG. 14, there is seen a side view of apparatus 100 with
the jaws open and the leads retracted from the jaws. Device 102 with
bonded TAB leads 104 is held by carrier 106. Carrier 106 is positioned in
adapter plate 110 which may be removed and replaced to allow for varying
sizes of carriers and devices. The bottom of device 102 is held by vacuum
pipette 112 which may be raised or lowered by linear stage 114 to
compensate for varying thicknesses. Linear stage 114 is attached to rotary
stage 116 to provide rotation when rotary stage 116 is activated.
Turntable 120 rotates in radial bearing 122 via a system of timing belts
and pulleys 123 (shown in FIG. 18) when rotary stage 116 is activated. The
timing belt system provides a means of device rotation (for excise and
forming adjacent sides of device 102) while the entire jaw assembly 124 is
open but poised around the device. This reduces cycle time by eliminating
the time needed to move jaw assembly 124 away from otherwise rotating
obstructions the rotary stage 116 would contain in order to rotate device
102.
Upper clamp blade 126 and lower clamp blade 130 are attached to upper clamp
jaw 132 and lower clamp jaw 134, respectively. Excise/form tool 136 and
excise blade 140 are attached to upper excise jaw 142 and lower excise jaw
144, respectively. Spring loaded lead clamp 146 slideably contacts excise
blade 140 and is also attached to lower excise jaw 144.
Lower excise jaw 144 can move vertically with respect to the upper excise
jaw 142 via linear bearings 148. This movement is actuated by a lead screw
152 when excise servo motor 154 is activated. (These components comprise
what is commonly known as a programmable, linear stage.)
Lower clamp jaw 134 can move vertically with respect to upper clamp jaw 132
via linear bearings 150 sliding on shafts 156. This movement is actuated
by lower actuator pin 160 (attached to lower excise jaw 144) contacting
surface 162 of lower clamp jaw 134 when lower excise jaw 144 moves as
previously described. Constant force springs 164 apply the force necessary
to keep surface 162 in contact with lower actuator pin 160.
Both upper excise jaw 142 and lower excise jaw 144 can move vertically on a
linear stage (not shown) when the vertical lead form servo motor 166 is
activated. When excise jaws 142 and 144 are open, clamp jaws 132 and 134
and shafts 156 also move as described with shafts 156 sliding in bearings
170. This is made possible by upper actuator pin 172 (attached to upper
excise jaw 142) contacting surface 174 of upper clamp jaw 132. The force
required for this contact is provided by gravity.
Excise jaws 142 and 144 can move horizontally with respect to clamp jaws
132 and 134 on a linear stage (not shown) when horizontal lead form servo
motor 176 is activated. This allows programming of the horizontal distance
between upper clamp blade 126 and excise/form tool 136, which in turn
dictates the horizontal distance between lower clamp blade 130 and excise
blade 140.
With reference now to FIG. 15, apparatus 100 is shown with the jaws open
and the leads in contact with the top clamp and excise/form tool.
Horizontal positioning of servo motor 180 is activated to move the entire
jaw assembly 124 until clamp blades 126 and 130 are in the programmed
horizontal position. Immediately thereafter, vertical lead form servo
motor 166 lowers jaw assembly 124 until upper clamp blade 126 reaches the
pre-set vertical clamp position; just touching a portion of leads 104 (or
any support ring thereon). This position is attained when surface 184 of
the clamp jaw assembly rests on surface 186 of vertical clamp position
adjuster 188. This position is set by manually turning adjustment knob
190. Once this position is attained, the clamp jaw assembly stops moving
and upper actuator pin 172 breaks contact with surface 174 of upper clamp
jaw 132. The force (gravity) which once held surface 174 in contact with
upper actuator pin 172 now holds surface 184 in contact with surface 186.
The excise jaw assembly is further lowered so that excise/form tool 136
attains its programmed position; just touching a second portion of leads
104.
Referring now to FIG. 16, apparatus 100 is shown with the leads clamped,
excised and ready to be formed. Excise/servo motor 154 is activated to
raise lower excise jaw 144 and lower clamp jaw 134. As this occurs, lower
clamp blade 130 clamps a portion of leads 104 against upper clamp blade
126, and lower actuator pin 160 breaks contact with surface 162. Constant
force springs 164 which once held surface 162 in contact with lower
actuator pin 160 provide lead clamping force between clamp blades 126 and
130. Lower excise jaw 144 continues to raise until a second portion of
leads 104 is clamped between excise/form tool 136 and spring loaded lead
clamp 146. Lower excise jaw 144 continues to move until a third portion of
leads 104 is excised by excise blade 140 and excise/form tool 136. The
excise jaw assembly can now be moved in a programmed path to form leads
104 by coordinating the motion of vertical and horizontal lead form servo
motors 166 and 176, respectively.
Referring again to FIG. 14, after the leads are excised and formed
apparatus 100 releases the leads and resets for another operation. Servo
motor 154 lowers lower excise jaw 144 and lower clamp jaw 134 to release
leads 104. The excise jaw assembly then moves at a 45 degree angle (up and
right) via servo motors 166 and 176 to attain the depicted position.
Immediately thereafter, servo motor 176 stops while servo motor 166
continues to raise jaw assembly 124 just enough to clear carrier 106. Then
rotary stage 116 is activated to rotate turntable 120 via the pulley and
belt system 123 so that an adjacent side of device 102 is presented for
excise and lead form.
With reference now to FIGS. 17-18, apparatus 100 is further illustrated by
a top plan view and an isometric view, respectively.
EXPERIMENTS PERFORMED
An experimental prototype (different from the previously described
prototype) was designed and fabricated to test the programmable excise and
lead form apparatus of the present invention. The experimental prototype
was adapted to an existing programmable X-Y motion base (Hurco CNC milling
machine model KM3P) and also utilized a programmable indexer, Haus model
S5C to rotate the chips. All other tool positions were achieved with
micrometer driven positioners and pneumatic cylinders with manually
adjustable stops. Thus, the experimental prototype was not a stand alone
unit but did perform the basic sequence of operations required.
Once the experimental prototype was assembled, several experiments were
performed to test the quality of the excise. Using built in adjustments of
the mechanism, the cutting allowance was adjusted to achieve a lead shear
without burrs to near cross sectioning quality.
Devices with 328 leads on 4 mil (100 micron) pitch were chosen because of
the relative degree of difficulty. The tie bars were removed from 10 of
these devices using a tie bar punch before the devices were mounted in
super 35 mm carriers, Camtex part C-053-01. Once mounted in the carriers,
the devices were excised and face-up lead formed on the programmed
experimental prototype.
Each device was then mounted in a separate fixture with the leads extending
upward to facilitate measurement. Most leads maintained a lead pitch and
planarity within 0.3 mils to 0.5 mils. Since approximately 27% of the
pitch (or 1.10 mils) was the maximum acceptable displacement for high
yield outer lead bonding on these devices, these results were acceptable.
The present invention, therefore, is well adapted to carry out the objects
and attain the ends and advantages mentioned, as well as others inherent
therein. While presently preferred embodiments of the present invention
have been described for the purpose of disclosure, numerous other changes
in the details of construction, arrangement of parts, compositions and
materials selection, and processing steps can be carried out without
departing from the spirit of the present invention which is intended to be
limited only by the scope of the appended claims.
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